I have been using MP3Tag for at least eight years, and find it an invaluable tool. The two problems I experience are some FLAC files will: 1) Not take the Artwork (JPeG) at all; 2) Some files will take the Artwork and it shows in the individual files on the PC, BUT in both Instances the Artwork will not display in My HEOS Controller (Amazon Fire), and my Digital Audio Player.
The vast majority (850 out of 1000+ Albums) display the Artwork correctly. I would like to know how to correct this problem.

When writing tags for FLAC files, the program simily fails if the cover image file that is bigger than about 20mb.
I have been wrestling with the cover image which happens to be 35.6mb (PNG file), and the program tells me it cannot write the tag. I reduced the size to 24mb (JPG file) and it still fails to write the tag.
Is this limitation of FLAC tag structure?
....My guess is that not many people are that insane enough to put ultra high quality cover art files, but it would be great if this …

Other than File sizes, what else is there to check? I have tried creating a very small file: 23.5Kb; and medium size file: 76Kb and large files 998Kb with the same Artwork and tried on the DX120 without success. What is there in a JPEG image that would prevent it being read?